I have a 5 gallon bucket that was 1/2 filled with an H2SO4 solution (15% by volume). The solution also had 6051 aluminum rod that was sitting inside.

After sitting for several months, all of the water has evaporated and a portion of the aluminum tubing has corroded away. What is left is white crystal powder attached to the remaining aluminum.

Can someone tell me what this substance is? I'm guessing it is salt crystals attached to aluminum rod, but I'm no chemist! Assuming this is something other than salt, what is the best method of disposal (i.e. Bring it to hazardous waste disposal, dilute and flush, poor it in my garden , pour it in my neighbors garden )?

My Ph meter is broken, so I can't even check the Ph at the moment.

Thanks,
Marc

P.S. This question is not for a class. I do some anodizing as a hobby, but haven't done it in a while. The chemicals have sat unused during that time.

The white powder will be aluminium sulfate ...The aluminium has reacted with the acid giving off hydrogen ...aluminium sulphate is used in water treatment plants , so it is quite safe, and non toxic ... I would add lots of water and wash it down the drain .

One odd thing... I was able to get my hands on a ph meter and found that when the substance was mixed with water the ph was as low as 1! I used 3 gallons of baking soda and 10s of gallons of water, mixing it in an outdoor fountain, to bring it to 7ish and then flushed it.

Certainly we would expect the residue to be acidic , the crystals must retain some moisture and some sulfuric acid ...

Ph 1 sounds very acidic , but a lemon has Ph 2 , so it's not too deadly ...good idea to neutralise it with baking soda , although I don't think drains are too worried about Ph , since it used to be common practice to clear blocked sink pipes by putting pure sodium hydroxide pellets down them !!! ... once the fluid hits the sewers Ph is quickly returned to neutral ...